Tanning with organic isocyanates in a nonaqueous medium



Patented Sept. 26, 1950 TANNING WITH ORGANIC ISOCYANA'EES IN ANONAQUEOUS MEDIUM Robert C. Putnam, Marbleheafl, Mass., assignor toUnited Shoe Machinery Corporation, Flemington, N. .L, a corporation ofNew Jersey 7 No Drawing. Application August 14., 19%,

Serial No. 768,713

6 Claims. (01. 8-94.33)

My invention relates to the treatment of hides and skins.

In the well-known chrome tanning process, a skin or hide pretreated toremove hair and treated by various other steps such as hating andpickling, is immersed for an extended period in a solution of basicchromium sulphate. Ordinarily this chromium treatment of the skin orhide is carried on in a "paddle or a drum during the chrome treatingperiod and is then removed from the paddle or drum and aged for a periodof from severalhours up to two days.

In the vegetable tanning process, dehaired and otherwise pretreatedskins or hides are subjected to various steps including a prolongedsoaking treatment in a solution containing various vegetable extracts.Tanning by the vegetable method occupies a period of several weeks andinvolves extensive handling of the hides.

By either of these common methods of tanning, extended periods of timeare required so that to insure continuous production of leather 9. verylarge number of skins or hides must be maintained in various stages oftanning. Investment in skins or hides and in treating tanks, vats, orother treating equipment is large so that the cost of the ultimateleather is high.

It is an important feature of my invention to convert skin and hidematerial to a stable nonputrescible leather-like condition by a shortand simple treatment of the skin or hide materials with a new type ofreagent. By my new process there is formed a tough, pliable productsimilar to leather in appearance and in many other properties. The newproduct will withstand prolonged soaking in water without markedshriveling or hardening even at relatively high temperatures, and isexceptionally resistant to mold growth.

I have discovered that skins or hides may be converted to this novelleather-like material by drying the skin or hide material and contactingthe dried material with certain isocyanates. These isocyanates areordinarily employed in the form of solutions which readily penetrate theskin or hide. I have made the further discovery that a productpossessing increased softness and flexibility and an improved appearanceis formed where certain special solvents are employed in combinationwith the active treating agents.

For treatment according to the process of the present invention, I havefound that bated or pickled skins or hides, for example calfskins orsteer hides, are very satisfactory. For most satistactory treatment, thehide or skin should have a pH of between about 5 and about '7 prior totreatment. However, skins or hides having a pH somewhat outside theseapproximate limits may be treated.

Skins or hides of animals generally used for making leather may betreated according to the process of the present invention. In thespecification the terms skin or skin material are to be understood intheir broad sense as including these materials. The term hide in theclaims is intended to include both skins and hides in the condition inwhich they are normally employed for tanning treatment.

Where a pickled material is used, it is first subjected to aconventional depickling operation. The depickled skin is then immersedin water with agitation to remove dissolved salts and other solublematerials. A suitable treatment .period may range from around 2 hoursfor calfskin to 4 hours for a steer skin.

The depickled and soaked skin is then dried to a moisture content whichmay be between about 10 and about 15%. This moisture content isdetermined by comparison with the weight of the skin when subjected to afurther drying for 16 hours in air at C. It has been found that dryingis most satsifactorily accomplished by the action of solvents, forexample, acetone, methyl acetate (acetate of the monomethyl ether ofethylene glycol), isopropyl alcohol, dioxane, methyl Cellosolve acetateor other solvent which will remove the water without seriously harmingthe skin. This drying may be effected by leaving the skin immersed in anagitated bath of the solvent overnight. The solvent is then removed fromthe skin, suitably by evaporation in a stream of dry, warmair.

The above is but one of many conceivable methods for treatment of a skinprior to the treatment with my new agents. Modifications will be readilyapparent to persons familiar with the handling of skins. For example, abated skin need not be subject to the depickling and washing operationsabove outlined.

The dried skin or hide is immersed in a body of the liquid treatingagent and is maintained in the liquid for a sufilcient period to convertthe skin or hide to the new leather-like condition.

I have found that the isocyanates of aliphatic hydrocarbons having from6 to 18 carbon atoms are effective to convert the skin or hide materialto a leather-like condition. Among the compounds in this class are hexylisocyanate, undecyl isocyanate and octadecyl isocyanate.

Other isocyanates which I have found effective to convert skin and hidematerial to leather-like condition are chloromethyl isocyanate,hexamethylene di-isocyanate, and 2,4-tolylene diisocyanate.

These treating agents are ordinarily employed as solutions in organicsolvents in order that they may penetrate well into the interior of theskin or hide material, and in order to avoid a too vigorous reactionbetween the material and the treating agent. Methyl Carbitol formal(formal of the monoethyl ether of diethylene glycol) has been foundparticularly satisfactory as a solvent for the treating agent, andsolutions comprising it give particularly soft and fine-appearing,leather-like products. Methyl Cellosolve" formal (formal of themonomethyl ether of ethylene glycol) has been used as a solvent withmany of applicants treating agents, and the solutions have been found togive very desirable products. A preferred range of concentrations ofsolutions is from about 10% to about 65% treating agent by volume basedon the volume of the solution.

The time of immersion of the skin in the treating agent varies with theweight and type of skin treated. Preferred times of treatment may varyfrom about one-half hour to about five hours. In the case of a calfskin,satisfactory action has been obtained by immersion of the prepared.dried, calfskin for about two hours at 130 F. in a 50% solution ofhexamethylene di-isocyanate in methyl Carbitol formal. In the case ofsteer hide, a four hour immersion in the same solution at 130 F. hasbeen found satisfactory.

Comparable effects on these materials have been obtained within the sametreating time using as treating agent a 50% solution of octadecylisocyanate in tri-chlorethylene at room temperature.

As illustrated above, the temperature of the treating bath may vary.Factors controlling the temperature include the boiling points and vaporpressure of the solvents and of the treating action desired.

After they above treatment, the skin is removed from the treating bathand is immersed in a solvent to remove soluble materials such as excessagent, reaction products and the like. Suitable solvents for this useare trichlorethylene, acetone and toluene.

The skin is removed from the solvent bath and is permitted to dry. Thedried skin is then placed in a neutralizing bath, which may be adepickling solution, until it reaches a pH of about '7 or other valuedepending upon the properties desired. This step is desirable in that italso serves to neutralize or decompose acid compounds which may haveformed within the skin. The skin is flnally washed to remove salts, andis then removed from the washin bath.

The treated skin may be subjected to such further treatments as desired,for example, dyeing, fat liquoring or stuffing, drying and surfacefinishing.

The following examples are given as illustrative of processes inaccordance with the present invention. It is to be understood that theinvention is not restricted to the reagents and procedural detailsdisclosed in these examples.

Example 1.A pickled calfskin was depickled by immersion in a solution ofsodium bicarbonate for an hour and was then washed in running water foran hour. The skin was then immersed overnight in acetone to dry the skinto a moisture content of about 10% as determined above. The dried skinwas then removed and the acetone evaporated by a blast of warm air. Theskin was immersed in a treating bath at room temperature for a period oftwo hours, the treating bath consisting of a solution of 50 parts byvolume of octadecyl isocyanate and 50 parts by weight oftrichlorethylene. The treated skin was removed from the treating bathand washed for two hours in a bath consisting only of tri-chlorethyleneafter which it is removed and the tri-chlorethylene allowed toevaporate. The skin was neutralized to a pH of about '7 by immersion ina bath of 5% sodium bicarbonate solution in water. The neutralized skinwas then removed from the sodium bicarbonate and washed in running waterfor two hours, at which time it was removed and found to be in aleather-like condition suitable for treatment by the usual operationsfollowing tanning of calfskin. The material so produced was found tohave exceptionally high resistance to water.

Example 2.--Pickled calfskin was depickled and dried as in the precedingexample and was subjected to a treating bath consisting of 20 parts byvolume of 2,4 tolylene di-isocyanate and parts by volume of methylCellosolve formal at 130 F. for two hours. The treated skin was washedin acetone for two hours, and was neutralized and washed as in thepreceding example. There was obtained a stable and non-putresciblematerial suitable for treatment by the usual operations employed aftertanning.

Example 3.-Pickled calfskin was depickled, washed, and dried as inExample 1 and was treated by immersion in a treating bath consisting of50 parts by volume of hexamethylene diisocyanate and methyl Carbitolformal at 130 F. for two hours. The treated skin was removed from thetreating bath, washed in acetone, neutralized and washed as in Example2. There was obtained a leather-like material in condition for furthertreatment by the usual operations following tanning.

Example 4.--A pickled calfskin was depickled. washed, and dried by theprocedure of Example 1 and was then immersed for two hours in a treatingbath consisting of 10 parts by volume of octadecyl isocyanate and partsby volume of methyl Cellosolve formal at a temperature of F. The treatedskin was removed from the bath, washed in acetone, neutralized andwashed in water as in Example 2. There was obtained a stable,non-putrescible, leather-like material in condition for treatment by theusual operations following tanning. The material is resistant toabsorption of water.

Example 5.A bated steer hide was dried by overnight immersion in acetoneto dry the skin to a moisture content of about 10% as determined above.The dried skin was then removed and the acetone evaporated by a blast ofwarm air. The skin was immersed in a treating bath at room temperaturefor five hours, the treating bath being a solution of 20 parts by volumeof octadecyl isocyanate and 80 parts by volume of tri-chlorethylene. Thetreated skin was removed from the treating bath and washed for two hoursin a bath consisting only of tri-chlorethylene, after which it wasremoved and the tri-chlorethylene allowed to evaporate. The skin wasthen neutralized and washed in running water as in Example 1. There wasobtained a stable, leather-like, non-putrescible material suitable fortreatment by the usual operations following tanning of a steer hide.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent of the United States is:

l. The method of tanning dried hides having a moisture content of fromto which comprises contactin the skins or hides with an organic solventsolution from 10% to 65% by volume based on the volume of the solutionof at least one member of the group consisting of isocyanates ofaliphatic hydrocarbons having from 6 to 18 carbon atoms, chloromethylisocyanate, hexamethylene di-isocyanate and 2,4-tolylene diisocyanate.

2. The method of tanning hides which comprises drying the hides by thesolvent action of an organic liquid to bring the moisture content downto from about 10% to about 15% and contacting the dried hides with anorganic solvent solution of at least one member of the group consistingof isocyanates of aliphatic hydrocarbons having from 6 to 18 carbonatoms, chloromethyl isocyanate, hexamethylene di-isocyanate and 2,4-tolylene di-isocyanate, the concentration of the solution being fromabout 10% to about 65% of treating agent based upon the volume of thesolution.

3. The method 01' tanning hides which comprises drying the hides by thesolvent action of an organic liquid to bring the moisture content downto from about 10% to about 15%, contacting the dried material with anorganic solvent solution of at least one member of the group consistingof isocyanates of aliphatic hydrocarbons having from 6 to 18 carbonatoms, chloromethyl isocyanate, hexamethylene di-isocyanate and2,4-tolylene di-isocyanate, the concentration of the solution being fromabout 10% to about 65% of treating agent based upon the weight of thesolution, removing uncombined compound by the action of a solvent,neutralizing acid compounds which may have formed within the hides,washing the hides to remove neutral salts and drying the hides.

4. The method of tanning hides which comprises drying the hides by thesolvent action of an organic liquid to bring the moisture content downto from 10% to about 15%, contacting the dried hides with a solution ofoctadecyl isocyanate in tri-chloroethylene, the concentration ofoctadecyl isocyanate in the solution being from about 10% to about 65%by volume based upon the volume of the solution, maintaining the hidesin contact with the solution for a period corresponding to from abouttwo hours for a calfskin to about four hours for a steer hide at atemperature of 130 F., removing uncombined octadecyl isocyanate by theaction of a solvent, neutralizing acid compounds which may have formedwithin the hides, washing the hides to remove neutral salts, and dryingthe hides.

5. The method of tanning hides which comprises drying the hides by thesolvent action of an organic liquid to bring the moisture content downto from about 10% to about 15%, contactin the dried hides with asolution of 2,4 tolylene di-isocyanate in the formal of the monomethylether of diethylene glycol, the concentration of 2,4- tolylenedi-isocyanate in the solution being from about 10% to about by volumebased upon the Weight of the solution, maintaining the hides in contactwith the solution for a period corresponding to from about two hours forcalfskin to about four hours for a steer hide at a temperature of F.,removing uncombined 2,4-tolylene di-isocyanate by the action of asolvent, neutralizing acid compounds which may have formed within thehides, washing the hides to remove neutral salts, and drying the hides.

6. The method of tanning hides which comprises drying the hides by thesolvent action of an organic liquid to bring the moisture content downto from about 10% to about 15%, contacting the dried hides with asolution of hexamethylene di-isocyanate in the formal of the monomethylether of diethylene glycol, the concentration of hexamethylenedi-isocyanate in the solution being from about 10% to about 65% byvolume based upon the weight of the solution, maintaining the hides incontact with the solution for a period corresponding to from about twohours for calfskin to about four hours for a steer hide at a temperatureof 130 F., removing uncombined hexamethylene di-isocyanate by the actionof a solvent, neutralizing acid compounds which may have formed withinthe hides, washing the hides to remove neutral salts, and drying thehides.

ROBERT C. PUTNAM.

REFERENCES CITED The following references are of record in the file oi.this patent:

UNITED STATES PATENTS Number Name Date 2,303,364 Schirm Dec. 1, 19422,319,057 Hanford May 11, 1943 FOREIGN PATENTS Number Country Date118,155 Australia Jan. 9, 1943 461,179 Great Britain Feb. 8, 1937 OTHERREFERENCES J our. Amer. Lea. Chem. Assn., article by Roddy., vol. 38,1943, pages -191.

BIOS Final Report No. 719, item No. 22 (BO No. 45,246), published Jan.31, 1947.

Chemie & Industrie, article by Curtis, June 1946, vol. 55, No. 6, pages436-438.

Gertificate 0! Correction Patent No. 2,523,326 September 26, 1950 ROBERTC. PUTNAM It is hereby certified that error appears in the rintedspecification of theabove numbered patent requiring correction as f0lows:

Column 3, line 44, after the word treating insert agents and the rate oftreating;

and that the said Letters Patent should be read as corrected above, sothat the same may conform to the record of the case in the PatentOfiice.

Signed and sealed this 24th day of April, A. D. 1951.

THOMAS F. MURPHY,

Assistant Oommz'asz'oner of Patents.

1. THE METHOD OF TANNING DRIED HIDES HAVING A MOISTURE CONTENT OF FROM10% TO 15% WHICH COMPRISES CONTACTING THE SKINS OR HIDES WITH AN ORGANICSOLVENT SOLUTION FROM 10% TO 65% BY VOLUME BASED ON THE VOLUME OF THESOLUTION OF AT LEAST ONE MEMBER OF THE GROUP CONSISTING OF ISOCYANATESOF ALIPHATIC HYDROCARBONS HAVING FROM 6 TO 18 CARBON ATOMS, CHLOROMETHYLISOCYANATE, HEXAMETHYLENE DI-ISOCYANATE AND 2,4-TOLYLENE DIISOCYANATE.